Yeah, a small GM tube (which is probably all you would want in a high field) would weigh very little, and could be read with a relatively simple circuit. Howev

Yeah, a small GM tube (which is probably all you would want in a high field) would weigh very little, and could be read with a relatively simple circuit. However, reading the associated reference, apparently they're using a "relay snake-like robot" to provide communications to the drone - and it is equipped with the ability to take dose measurements.